Impedance Matching Device

ABSTRACT

Provided is an impedance matching device for matching an impedance between a high-frequency power source and a load. The impedance matching device pertaining to the present invention is provided with: a matching circuit having variable capacitors, a capacitance of which is adjusted by an ON/OFF operation of a plurality of switches; a switch control unit for performing control for causing states of the switches of the variable capacitors to coincide with a target state in order to adjust the capacitance of the variable capacitors; and a switch state evaluation unit for evaluating whether a switch is in a state requiring suppression of a temperature increase. The switch control unit is configured so that when the switch state evaluation unit evaluates that a switch of the variable capacitors is in a state requiring suppression of a temperature increase, control is performed for suspending changing of a switch state of the switch for a set period and suppressing a temperature increase in the switch.

TECHNICAL FIELD

The present invention relates to an impedance matching device wherebyimpedance can be matched between a high-frequency power source and aload.

BACKGROUND ART

In order to eliminate reflection of electric power from a load andefficiently supply electric power to the load when electric power issupplied from a high-frequency power source to a plasma load or otherload, an impedance matching device is provided between thehigh-frequency power source and the load so that an output impedance ofthe high-frequency power source and an impedance of a circuit viewedfrom an output terminal of the high-frequency power source toward theload are matched. In the present specification, the impedance of thecircuit viewed from the output terminal of the high-frequency powersource toward the load is referred to as a load-side impedance.

This type of impedance matching device, which has been widely used inthe past, is provided with a mechanically operated variable capacitorprovided with an operating shaft for adjusting a capacitance thereof, aninductor constituting part of a matching circuit along with the variablecapacitor, a motor for operating the operating shaft of the variablecapacitor, and a control unit for controlling the motor so as to cause aposition of the operating shaft of the variable capacitor to coincidewith a target position, and impedance matching is performed in theimpedance matching device by controlling the position of the operatingshaft of the variable capacitor to coincide with a necessary positionthereof for achieving impedance matching, as disclosed in PatentDocument 1, for example.

However, when a mechanically operated variable capacitor is used, anability to increase a matching speed is limited, and a problem thereforearises that an ability of a matching operation to follow variations inimpedance deteriorates when high-frequency electric power is supplied toa load in which the impedance frequently varies, such as in the case ofa plasma load, reflected power increases, and electric power can nolonger be efficiently supplied to the load.

An electronically controlled impedance matching device has thereforebeen proposed in which, instead of a mechanically operated variablecapacitor, a variable capacitor is used that is capable of electroniccontrol and that has a structure in which a plurality of capacitanceelements are connected in parallel, each of the capacitance elementsbeing constituted from a capacitor and a capacitance adjustment switchcomprising a semiconductor element connected in series to the capacitor,and impedance matching can be rapidly performed by changing a state (ONstate or OFF state) of at least one of the capacitance adjustmentswitches provided to the variable capacitor each time a variation in theload-side impedance is detected, as disclosed in Patent Document 2.

PRIOR ART DOCUMENTS Patent Documents

[Patent Document 1] Japanese Laid-open Patent Application No.2010-198524

[Patent Document 2] Japanese Laid-open Patent Application No.2012-142285

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

In the configuration disclosed in Patent Document 2, when a load-sideimpedance has changed, impedance matching can be achieved by changing astate of at least one of capacitance adjustment switches provided to avariable capacitor and adjusting a capacitance of a variable capacitorto a necessary value for impedance matching. Since a capacitanceadjustment switch comprising a semiconductor element can be turned ONand OFF at high speed, the impedance matching device disclosed in PatentDocument 2 enables rapid matching of impedance between a high-frequencypower source and a load.

When high-frequency electric power is supplied to a load in which theimpedance frequently varies, such as in the case of a plasma load, inorder to increase the precision of impedance matching in an applicationof the impedance matching device disclosed in Patent Document 2, aperiod at which the load-side impedance is sampled must be shortened,and the capacitance of the variable capacitor must be finely adjusted.However, in a case in which an impedance of a load frequently varies,when the sampling period of the load-side impedance is shortened and thecapacitance of the variable capacitor of a matching circuit is adjustedeach time a variation in the load-side impedance is detected, at leastone of the series of capacitance adjustment switches provided to thevariable capacitor is then forced to turn ON and OFF at a highfrequency. In this case, when the load-side impedance continues to vary,due to increased switching loss in a semiconductor element constitutingpart of the capacitance adjustment switch that is caused to turn ON andOFF at high frequency, a junction temperature of the semiconductorelement increases, and there is a risk of thermal destruction of thecapacitance adjustment switch.

In order to avoid this problem, it is possible to lengthen a period atwhich the load-side impedance is sampled, and to lengthen a period atwhich a switch state of the capacitance adjustment switch is changed.However, when the period at which the load-side impedance is sampled islengthened, the capacitance of each variable capacitor of the matchingcircuit can no longer be adjusted with high precision to follow anactual variation of the load-side impedance, and the matching operationcan no longer be made to follow the variation in the load-sideimpedance, thus leading to an unavoidable decrease in matchingprecision.

An object of the present invention is to make it possible to reliablyprotect a capacitance adjustment switch without significantly decreasinga precision of impedance matching when a load-side impedance varies at ahigh frequency, in an impedance matching device for matching an outputimpedance of a high-frequency power source and a load-side impedanceusing a matching circuit that employs an electronically operatedvariable capacitor in which a capacitance thereof is adjusted by theON/OFF operation of capacitance adjustment switches comprisingsemiconductor elements.

Means to Solve the Problems

The present invention is an impedance matching device for matching anoutput impedance of a high-frequency power source and a load-sideimpedance, which is an impedance viewed from an output terminal of thehigh-frequency power source toward a load. In the present invention, inorder to achieve the abovementioned object, the impedance matchingdevice comprises: a matching circuit disposed between the high-frequencypower source and a load, the matching circuit being provided with atleast one variable capacitor having a structure in which a plurality ofcapacitance elements are connected in parallel, the capacitance elementsbeing constituted from a capacitor and a capacitance adjustment switchconnected in series, and the capacitance adjustment switch comprising asemiconductor element; a matching calculation unit for performing, at aset period, a matching calculation for determining, as a target switchstate, a state in which the capacitance adjustment switches provided tothe matching circuit should take in order for the output impedance ofthe high-frequency power source and the load-side impedance to bematched; a switch control unit for performing control for causing switchstates of the capacitance adjustment switches provided to the matchingcircuit to coincide with the target switch state; and a switch stateevaluation unit for evaluating whether at least one of the capacitanceadjustment switches provided to the matching circuit is in a staterequiring suppression of a temperature increase; the switch control unitbeing configured so that when an evaluation is made by the switch stateevaluation unit that at least one of the capacitance adjustment switchesprovided to the matching circuit is in a state requiring suppression ofa temperature increase, the at least one capacitance adjustment switchprovided to the matching circuit is designated as a protection-objectswitch, and temperature increase suppression control for suppressing atemperature increase in the protection-object switch by stoppingswitching operation of the protection-object switch or reducing afrequency with which the protection-object switch performs switchingoperation is performed for a set temperature increase suppressionperiod.

Through the present invention, it is possible to eliminate heatgeneration or reduce the amount of heat generated from theprotection-object switch for the duration of the temperature increasesuppression period and to suppress a temperature increase therein, andappropriate protection of the capacitance adjustment switches cantherefore be achieved. For a period other than the temperature increasesuppression period, control is also performed for causing a switch stateof the series of capacitance adjustment switches provided to thematching circuit to coincide with the target switch state determined bythe matching calculation unit, and it is therefore possible to protectthe capacitance adjustment switches without significantly decreasingprecision of impedance matching between the high-frequency power sourceand the load.

In an aspect of the present invention, the matching calculation unit isconfigured so as to sample, at a set sampling period, a parameter thatreflects the load-side impedance and to perform the matching calculationeach time the parameter is sampled.

In an aspect of the present invention, at least one of the capacitanceadjustment switches provided to the matching circuit is designated as amonitoring-object switch, and by monitoring a switch state of themonitoring-object switch, an evaluation is made as to whether at leastone of the capacitance adjustment switches provided to the matchingcircuit is in a state requiring suppression of a temperature increase.In this case, a switch state evaluation means is provided with changefrequency evaluation means for evaluating whether a switch state changefrequency is equal to or greater than a set evaluation reference value,the switch state change frequency being a number of times that a switchstate of the monitoring-object switch is changed from an ON state to anOFF state or from the OFF state to the ON state in a set evaluationreference time, and the switch state evaluation unit is configured so asto evaluate that at least one of the capacitance adjustment switchesprovided to the matching circuit is in a state requiring suppression ofa temperature increase when an evaluation is made by the changefrequency evaluation means that the switch state change frequency of themonitoring-object switch is equal to or greater than the evaluationreference value.

In another aspect of the present invention, at least one variablecapacitor provided to the matching circuit is designated as amonitoring-object variable capacitor, and at least one capacitanceadjustment switch provided to the monitoring-object variable capacitoris designated as the monitoring-object switch.

In another aspect of the present invention, a number of times that thetarget switch state of the monitoring-object switch is changed by thematching calculation unit in a set evaluation reference time isdesignated as the switch state change frequency of the monitoring-objectswitch.

In the above description, the switch state evaluation means isconfigured so as to evaluate whether at least one of the capacitanceadjustment switches provided to the matching circuit is in a staterequiring suppression of a temperature increase on the basis of afrequency with which the state of the monitoring-object switch ischanged, but the present invention is not limited to such aconfiguration of the switch state evaluation means.

For example, a configuration may also be adopted in which the switchstate evaluation unit is provided with load-side impedance occurrencefrequency detection means for detecting, as a load-side impedancevariation occurrence frequency, a number of times that a variationgreater than or equal to a set size occurs in the load-side impedance ina set evaluation reference time, and load-side impedance variationoccurrence frequency evaluation means for evaluating whether thedetected load-side impedance variation occurrence frequency is equal toor greater than a set evaluation reference value, and the switch stateevaluation unit is configured so as to evaluate that at least one of thecapacitance adjustment switches provided to the matching circuit is in astate requiring suppression of a temperature increase when an evaluationis made by the load-side impedance variation occurrence frequencyevaluation means that the load-side impedance variation occurrencefrequency is equal to or greater than the set evaluation referencevalue.

The switch state evaluation unit may also be configured so as toevaluate that at least one of the capacitance adjustment switchesprovided to the matching circuit is in a state requiring suppression ofa temperature increase when a temperature that reflects a temperature ofthe capacitance adjustment switches provided to the matching circuit isequal to or greater than a set evaluation reference value.

In the present invention, the evaluation reference time and theevaluation reference value are not necessarily fixed, and the evaluationreference time and/or the evaluation reference value may also be changedin accordance with the temperature that reflects the temperature of thecapacitance adjustment switches, or another appropriate parameter. Forexample, the evaluation reference value may be made smaller the higherthe temperature that reflects the temperature of the capacitanceadjustment switches is, and the evaluation reference time may be madeshorter the higher the temperature that reflects the temperature of thecapacitance adjustment switches is.

The temperature increase suppression period is also not necessarilyfixed, and the duration of the temperature increase suppression periodmay be changed in accordance with a size of a parameter such as thetemperature that reflects the temperature of the capacitance adjustmentswitches. For example, the temperature increase suppression period maybe made longer the higher the temperature that reflects the temperatureof the capacitance adjustment switches is.

Yet other aspects of the present invention will be made clear in thedescription given below of the best mode for carrying out the invention.

Advantageous Effects of the Invention

In the present invention, a switch state evaluation unit is provided forevaluating whether at least one of a capacitance adjustment switchesprovided to a matching circuit is in a state requiring suppression of atemperature increase, at least one of the capacitance adjustmentswitches provided to the matching circuit is designated as aprotection-object switch when an evaluation is made by the evaluationunit that at least one of the capacitance adjustment switches providedin the matching circuit requires suppression of a temperature increase,and temperature increase suppression control for suppressing atemperature increase in the protection-object switch by stoppingswitching operation of the protection-object switch or reducing afrequency with which the protection-object switch performs switchingoperation is performed for a set temperature increase suppressionperiod; therefore, it is possible to eliminate heat generation or reducean amount of heat generated from the protection-object switch for aduration of the temperature increase suppression period and to suppressa temperature increase therein, and appropriate protection of thecapacitance adjustment switches can therefore be achieved. For a periodother than the temperature increase suppression period, control is alsoperformed for causing a switch state of a series of capacitanceadjustment switches provided to the matching circuit to coincide with atarget switch state determined by a matching calculation unit, and it istherefore possible to protect the capacitance adjustment switcheswithout significantly decreasing a precision of impedance matchingbetween a high-frequency power source and a load.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram illustrating a circuit structure of anembodiment of an impedance matching device according to the presentinvention;

FIG. 2 is a block diagram illustrating an example configuration of acontrol unit used in an embodiment of the present invention;

FIG. 3 is a block diagram illustrating another example configuration ofthe control unit used in an embodiment of the present invention;

FIG. 4 is a block diagram illustrating yet another example configurationof the control unit used in an embodiment of the present invention;

FIG. 5 is a block diagram illustrating yet another example configurationof the control unit used in an embodiment of the present invention;

FIG. 6 is a block diagram illustrating yet another example configurationof the control unit used in an embodiment of the present invention;

FIG. 7 is a block diagram illustrating yet another example configurationof the control unit used in an embodiment of the present invention;

FIG. 8 is a block diagram illustrating yet another example configurationof the control unit used in an embodiment of the present invention;

FIG. 9 is a block diagram illustrating yet another example configurationof the control unit used in an embodiment of the present invention;

FIG. 10 is a flowchart illustrating an example of an algorithm of aprogram executed by a microprocessor constituting part of the controlunit used in the embodiment illustrated in FIG. 2;

FIG. 11 is a flowchart illustrating another example of the algorithm ofa program executed by a microprocessor constituting part of the controlunit used in the embodiment illustrated in FIG. 2;

FIG. 12 is a time chart for explaining an operation of an embodiment ofthe present invention; and

FIG. 13 is another time chart for explaining the operation of anembodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of an impedance matching device according to the presentinvention will be described below with reference to the accompanyingdrawings. FIG. 1 illustrates a circuit configuration of an embodiment ofthe impedance matching device according to the present invention. InFIG. 1, a reference numeral 1 refers to a high-frequency power sourcefor outputting high-frequency electric power, 2 refers to a load towhich high-frequency electric power is supplied from the high-frequencypower source 1, 3 refers to an impedance matching device that performsan operation to match a load-side impedance, which is the impedanceviewed from an output terminal of the high-frequency power source 1toward the load, to an output impedance of the high-frequency powersource 1, the impedance matching device being provided between thehigh-frequency power source 1 and the load 2, and 4 refers to ahigh-frequency detection unit for detecting a parameter used tocalculate the impedance viewed from the output terminal of thehigh-frequency power source 1 toward the load. The structure of eachcomponent is described below.

<High-Frequency Power Source>

The high-frequency power source 1 is constituted from, for example, ahigh-frequency signal generating unit for generating a signal having afrequency equal to the frequency of the electric power supplied to theload, and a power amplifier for amplifying an output of thehigh-frequency signal generating unit.

<Load>

In the present embodiment, the load 2 is a plasma load used in asemiconductor processing device or the like. The plasma load is providedwith a chamber in which an object to be processed is accommodated, and aplasma generating electrode disposed in the chamber, for example, andwhen high-frequency electric power is supplied to the plasma generatingelectrode, a gas in the chamber is ionized and a plasma is generated.The impedance of the plasma load always varies, and the impedancematching device 3 is therefore required to perform impedance matching athigh speed.

<Matching Circuit>

Various embodiments of a matching circuit 31 according to the presentinvention are possible, but in the present embodiment, the matchingcircuit 31 is constituted from: a first variable capacitor VC1, one endof which is connected to a non-ground-side output terminal of thehigh-frequency power source 1 through the high-frequency detection unit4 and the other end of which is grounded; a second variable capacitorVC2, one end of which is connected to the one end of the first variablecapacitor VC1; and an inductor L1 connected between the load 2 and theother end of the second variable capacitor VC2.

In order to facilitate adjustment of a capacitance of each of thevariable capacitors, each of the variable capacitors has a plurality ofcapacitance elements constituted from a capacitor and a capacitanceadjustment switch connected in series, the capacitance adjustment switchcomprising a semiconductor element, and each of the variable capacitorsis preferably an electronically operated variable capacitor having astructure in which the plurality of capacitance elements are connectedto each other in parallel. When variable capacitors having such astructure are used, the capacitance of the variable capacitors can beadjusted, as appropriate, by changing a combination of ON/OFF states ofa series of capacitance adjustment switches provided to the plurality ofcapacitance elements connected to each other in parallel.

Each of the variable capacitors VC1 and VC2 used in the presentembodiment has a structure in which first through n^(th) (n being aninteger of 2 or greater) capacitance elements Ce1-Cen are connected toeach other in parallel, the capacitance elements Ce1-Cen being formed byconnecting, in series, first through n^(th) capacitance adjustmentswitches S1-Sn each comprising a semiconductor element to first throughn^(th) capacitors C1-Cn, respectively. When the variable capacitors VC1and VC2 are constituted in this manner, the capacitance of each variablecapacitor becomes equal to a total capacitance value of the capacitorsconnected in series to the capacitance adjustment switches that are inan ON state. For example, the capacitance of the variable capacitorswhen the first capacitance adjustment switch S1 and the thirdcapacitance adjustment switch S3 are in the ON state and the othercapacitance adjustment switches are in an OFF state is equal to thetotal value of the capacitance of the capacitor C1 and the capacitanceof the capacitor C3.

In the present embodiment, the first through n^(th) capacitanceadjustment switches S1-Sn comprise PIN diodes that can be ON/OFFcontrolled at high speed. Each of the PIN diodes is placed in the OFFstate by application of a reverse-directed direct-current voltagebetween an anode and cathode thereof from a driver circuit notillustrated in the drawings, and is placed in the ON state byapplication of a constant forward-directed direct-current voltagebetween the anode and cathode thereof. The PIN diodes are in alow-impedance state (ON state) when a fixed DC current is flowingtherethrough in a forward direction. When the PIN diodes are in the ONstate, a high-frequency current can flow in both directions through thediodes.

When the variable capacitors are constituted as illustrated in FIG. 1,the capacitance of the variable capacitors VC1 and VC2 can be adjustedin two n^(th)-power steps by making the capacitances of the firstthrough n^(th) capacitors C1-Cn dissimilar and appropriately selectingthe state (ON state or OFF state) of each of the first through n^(th)capacitance adjustment switches S1-Sn.

In order to facilitate understanding of a relationship between thestates of the first through n^(th) capacitance adjustment switches S1-Snand the capacitances of the variable capacitors VC1 and VC2, when thefirst through n^(th) first through n^(th) capacitors C1-Cn are made tocorrespond to first through n^(th) digits, respectively, of an n-bitbinary number, the first digit and the n^(th) digit thereof being aleast significant digit and a most significant digit, respectively, ofthe binary number, and the capacitance of the first capacitor C1 as thesmallest capacitance among the capacitances of the first through n^(th)first through n^(th) capacitors C1-Cn is designated as Cmin, forexample, the capacitances of each of the first through n^(th) capacitorsC1-Cn are set so that the capacitance Ck of the k^(th) (k=1 to n)capacitor (the capacitor corresponding to the k^(th) digit from theleast significant digit of the binary number) has a value determined byequation (1) below.

Ck=Cmin·2^(k-1)  (1)

In the above equation, k−1 is a bit number indicating a bit position ofthe bit of the k^(th) digit from the least significant digit of thebinary number to which the k^(th) capacitor corresponds. When thecapacitances of the first through n^(th) capacitors are established in amanner described above, 2^(n) capacitances (capacity of a syntheticcapacitor of C1-Cn) differing in value by Cmin each can be obtained bychanging the combination of states (ON state or OFF state) of the firstthrough n^(th) capacitance adjustment switches S1-Sn.

For example, when n=4, Cmax=1 pF, a first capacitance adjustment switchS1 through fourth capacitance adjustment switch S4 are made tocorrespond to a first through fourth digits, respectively, of afour-digit binary number, and the capacitances of the capacitors C1through C4 are set to 1, 2, 4, and 8 [pF], respectively, in accordancewith equation (1), a variable capacitor can be obtained in which thecapacitance thereof can have 2⁴ (16 in the present example) values (0 to15 [pF] in the present example) differing by Cmin [pF] (1 [pF] in thepresent example) each, as shown in Table 1 below.

TABLE 1 Digit number k 4 3 2 1 Capacitor (Electrostatic capacity) C4 C3C2 C1 Synthetic (8) (4) (2) (1) capacitor Switch element capacity S4 S3S2 S1 [pF] Binary 0 0 0 0 0 number 0 0 0 1 1 State of 0 0 1 0 2 switch 00 1 1 3 elements 0 1 0 0 4 S1-S4 0 1 0 1 5 0: OFF 0 1 1 0 6 1: ON 0 1 11 7 1 0 0 0 8 1 0 0 1 9 1 0 1 0 10 1 0 1 1 11 1 1 0 0 12 1 1 0 1 13 1 11 0 14 1 1 1 1 15

When 10 capacitors are provided (n=10), the capacitance of the firstcapacitor C1 is set to 1 [pF], and the capacitances of the capacitorsC1, C2, and so on are set so as to double in sequence 1 pF, 2 pF, 4 pF,8 pF, and so on with the capacitance of the 10^(th) capacitor being 512pF, for example, the capacitance of the variable capacitor can beadjusted in 1 pF units from 0 pF to 1023 pF.

In the present embodiment, the state (ON state or OFF state) referred toas the “target switch state” is a state in which the series ofcapacitance adjustment switches provided to the variable capacitorsshould take in order for the variable capacitors to have the capacitancethat is necessary for matching the impedance between the high-frequencypower source and the load. When a relationship between a binary numberand the capacitors is established as described above, the target switchstate is specified by a binary number having a number of digits equal tothe number of capacitance adjustment switches in the series thereofprovided to the variable capacitor.

For example, the variable capacitors are constituted from fourcapacitance elements, first through fourth capacitance adjustmentswitches S1-S4 are provided to the variable capacitors, the firstcapacitance adjustment switch S1 through fourth capacitance adjustmentswitch S4 are made to correspond to the first through fourth digits,respectively, of a four-digit binary number, and the four-digit binarynumber and the capacitances of the variable capacitors are relatedaccording to the relationship illustrated in Table 1. In this case, thetarget capacitance of the variable capacitor VC1 that is needed so thatthe impedance viewed from the output terminal of the high-frequencypower source 1 toward the load is matched to the output impedance of thehigh-frequency power source 1 is 10 pF, and the target capacitance ofthe variable capacitor VC2 is 5 pF. In this case, the target switchstate to be assumed by the fourth capacitance adjustment switch S4, thethird capacitance adjustment switch S3, the second capacitanceadjustment switch S2, and the first capacitance adjustment switch S1 ofthe variable capacitor VC1 is specified by the four-digit binary number“1010,” and the target switch state to be assumed by the fourthcapacitance adjustment switch S4, the third capacitance adjustmentswitch S3, the second capacitance adjustment switch S2, and the firstcapacitance adjustment switch S1 of the variable capacitor VC2 isspecified by the four-digit binary number “0101.”

<High-Frequency Detection Unit>

The high-frequency detection unit 4 illustrated in FIG. 1 is a componentfor detecting a parameter used to calculate the load-side impedance. Ahigh-frequency voltage and high-frequency current supplied from thehigh-frequency power source 1 to the load 2, and a phase differencebetween the high-frequency voltage and high-frequency current, forexample, may be used as parameters that reflect the load-side impedance,and traveling-wave power and reflected-wave power detected at an outputend of the high-frequency power source 1 may also be used. Thehigh-frequency detection unit 4 is provided with a directional coupleror the like and is configured so as to be able to detect the aboveparameters. In the present embodiment, the high-frequency voltage andhigh-frequency current presented to the load 2 from the high-frequencypower source 1, and the phase difference between the high-frequencyvoltage and high-frequency current, are detected from the high-frequencydetection unit 4 as parameters that reflect the load-side impedance.

<Control Unit>

An example of a configuration of a control unit 32 used in the presentembodiment is illustrated in FIG. 2. The control unit 32 illustrated inFIG. 2 is constituted from a matching calculation unit 32A, a switchstate evaluation unit 32B, and a switch control unit 32C. Although notshown in FIG. 2, the control unit 32 is provided with a pulse generatorfor generating a sample pulse Ps at a fixed sampling period t1, asillustrated in FIG. 12(A). A structure of the matching calculation unit32A, the switch state evaluation unit 32B, and the switch control unit32C constituting the control unit 32 will be described below.

<Matching Calculation Unit>

The matching calculation unit 32A illustrated in FIG. 2 is a componentfor performing, at a set period, a matching calculation for determining,as the target switch state, a state in which the capacitance adjustmentswitches provided to the matching circuit 31 should be set so as tomatch together the output impedance of the high-frequency power source 1and the impedance of the circuit (load-side impedance) viewed from theoutput terminal of the high-frequency power source toward the load 2. Inthe present embodiment, a parameter that reflects the load-sideimpedance is sampled at a sampling period set from the high-frequencydetection unit 4, and the matching calculation unit 32A is configured soas to perform the matching calculation each time the parameter issampled.

A high-frequency voltage and high-frequency current supplied from thehigh-frequency power source 1 to the load 2, and the phase differencebetween the high-frequency voltage and high-frequency current, forexample, may be used as parameters that reflect the impedance viewedfrom the output terminal of the high-frequency power source toward theload. A traveling-wave power and reflected-wave power detected at theoutput end of the high-frequency power source, or a reflectioncoefficient of the reflected-wave power, may also be used as theabovementioned parameter.

In the present embodiment, the matching calculation unit 32A isconstituted from a load-side impedance calculation means 32A1, acapacitance calculation means 32A2, and a target switch statedetermination means 32A3. In the load-side impedance calculation means32A1, the parameter reflecting the load-side impedance is sampled fromthe high-frequency detection unit 4 each time that a pulse generator(not illustrated in the drawings) generates a sample pulse Ps (see FIG.12(A)) at the fixed period t1, and the load-side impedance is calculatedeach time the parameter is sampled.

The capacitance calculation means 32A2 is a means for calculating thecapacitance that each of the variable capacitors VC1 and VC2 of thematching circuit 31 should have in order to match the load-sideimpedance calculated by the load-side impedance calculation means 32A1to the output impedance of the high-frequency power source 1.

The target switch state determination means 32A3 is a means fordetermining, as the target switch state of the first through n^(th)capacitance adjustment switches S1-Sn connected in series to the firstthrough n^(th) capacitors C1-Cn, respectively, constituting the variablecapacitor VC1, the state (ON/OFF state) in which the capacitanceadjustment switches S1-Sn of the variable capacitor VC1 should take inorder to make the capacitance of the variable capacitor VC1 equal to (orinfinitely close to) the capacitance calculated by the capacitancecalculation means 32A2, and determining, as the target switch state ofthe first through n^(th) capacitance adjustment switches S1-Sn connectedin series to the first through n^(th) capacitors C1-Cn, respectively,constituting the variable capacitor VC2, the state in which thecapacitance adjustment switches S1-Sn of the variable capacitor VC2should take in order to set the capacitance of the variable capacitorVC2 to the capacitance calculated by the capacitance calculation means32A2.

<Switch State Evaluation Unit>

The switch state evaluation unit 32B is a means for evaluating whetherat least one of the capacitance adjustment switches provided to thematching circuit 31 is in a state requiring suppression of a temperatureincrease. A state requiring suppression of a temperature increase in acapacitance adjustment switch is defined as a state in which atemperature of a junction of a semiconductor element constituting thecapacitance adjustment switch exceeds an allowable limit and there is arisk of destruction of the capacitance adjustment switch if ON/OFFoperation of the switch state of the capacitance adjustment switch iscontinued in that temperature condition.

In the present embodiment, at least one of the capacitance adjustmentswitches S1-Sn provided to the variable capacitor VC1 and thecapacitance adjustment switches S1-Sn provided to the variable capacitorVC2 is designated as a monitoring-object switch, and the switch stateevaluation unit 32B is configured so as to evaluate whether at least onemonitoring-object switch is in a state requiring suppression of atemperature increase.

The evaluation as to whether a capacitance adjustment switch is in astate requiring suppression of a temperature increase can be performedby monitoring a parameter that is correlated with the temperature of ajunction of a semiconductor element constituting the capacitanceadjustment switch. Consequently, the switch state evaluation unit 32Bmonitors a parameter that is correlated with the temperature of ajunction of a monitoring-object switch, and can be configured so as toevaluate whether at least one monitoring-object switch is in a staterequiring suppression of a temperature increase on the basis of theparameter.

The frequency with which the load-side impedance varies by a set valueor greater, the frequency with which the switch state of a capacitanceadjustment switch is changed, a temperature of a specific portionreflecting a temperature of a capacitance adjustment switch provided tothe matching circuit, or another parameters, for example, can be used asa parameter that is correlated with the temperature of a junction of acapacitance adjustment switch. A temperature of a substrate on which acapacitance adjustment switch is mounted, a temperature of asemiconductor element package constituting a capacitance adjustmentswitch, or a temperature of a heat sink devised to dissipate heat from acapacitance adjustment switch, for example, can be used as a temperaturethat reflects the temperature of a capacitance adjustment switchprovided to the matching circuit.

In the embodiment illustrated in FIG. 2, the frequency (switch statechange frequency) with which the switch state of a capacitanceadjustment switch is changed from the ON state to the OFF state or fromthe OFF state to the ON state is used as the parameter that iscorrelated with the temperature of a junction of the capacitanceadjustment switch.

The switch state evaluation unit 32B illustrated in FIG. 2 is providedwith a change frequency evaluation means 32B1 for evaluating whether theswitch state change frequency of a monitoring-object switch is equal toor greater than a set evaluation reference value, the monitoring-objectswitch being at least one of the capacitance adjustment switchesprovided to the matching circuit, and the switch state change frequencybeing the frequency with which the switch state of the monitoring-objectswitch is changed from the ON state to the OFF state or from the OFFstate to the ON state, and the switch state evaluation unit 32B isconfigured so that when the change frequency evaluation means 32B1determines that the switch state change frequency of at least onemonitoring-object switch is equal to or greater than the evaluationreference value, the switch state evaluation unit 32B determines that atleast one of the capacitance adjustment switches provided to thematching circuit 31 is in a state requiring suppression of a temperatureincrease.

In the present embodiment, the switch state change frequency of themonitoring-object switch is a number of times that the switch state ofthe monitoring-object switch is changed in a set evaluation referencetime. The number of times that the switch state of the monitoring-objectswitch is changed in the evaluation reference time can be detected bycounting the number of times that the switch state of themonitoring-object switch is actually changed in the set evaluationreference time, or by counting the number of times that the matchingcalculation unit 32A changes the target switch state of themonitoring-object switch in the set evaluation reference time.

The “evaluation reference time” used when determining the switch statechange frequency of a capacitance adjustment switch and the “evaluationreference value” used when evaluating whether a capacitance adjustmentswitch is in a state requiring suppression of a temperature increase canbe determined by conducting an experiment in which an impedance matchingoperation is performed while the parameters are changed in various ways,and a temperature of the capacitance adjustment switch is measured.

In the above description, the monitoring-object switch is at least oneof all of the capacitance adjustment switches provided to the matchingcircuit 31, but a configuration may also be adopted in which at leastone of the variable capacitors provided to the matching circuit 31 isselected as a “monitoring-object variable capacitor,” and at least onecapacitance adjustment switch provided to the monitoring-object variablecapacitor is designated as the monitoring-object switch.

Specifically, the change frequency evaluation means 32B1 can beconfigured so that at least one of the variable capacitors provided tothe matching circuit 31 is designated as a monitoring-object variablecapacitor, and at least one of the capacitance adjustment switchesprovided to the monitoring-object variable capacitor is designated asthe monitoring-object switch. In this case as well, the switch stateevaluation unit 32B is configured so that when the change frequencyevaluation means determines that the switch state change frequency of atleast one monitoring-object switch is equal to or greater than theevaluation reference value, the switch state evaluation unit 32Bdetermines that at least one of the capacitance adjustment switchesprovided to the matching circuit is in a state requiring suppression ofa temperature increase.

<Monitoring-Object Variable Capacitor and Monitoring-Object Switch>

When a plurality of variable capacitors are provided to the matchingcircuit in the impedance matching device, it is not always the case thatfrequent adjustments are made to the capacitances of all the variablecapacitors when the load-side impedance changes, and it is sometimes thecase that frequent adjustments are made to the capacitances of only someof the variable capacitors.

Moreover, the frequency with which the switch state is changed is notthe same for each of the plurality of capacitance adjustment switchesprovided to the variable capacitors, and the switch state changefrequency of a capacitance adjustment switch whose switch state ischanged (turned ON or OFF) during adjustment of the value of lower-orderdigit of the capacitance of a variable capacitor is greater than theswitch state change frequency of a capacitance adjustment switch whoseswitch state is changed during adjustment of the numerical value of ahigher-order digit of the capacitance of a variable capacitor.

When it is known that there is a difference in the frequency with whichthe capacitances of the plurality of variable capacitors provided to thematching circuit are adjusted, there is no need to use the capacitanceadjustment switches provided to all the variable capacitors asmonitoring-objects; a configuration may be adopted in which the variablecapacitor having the higher frequency of capacitance adjustment is usedas the monitoring-object variable capacitor, and the switch state changefrequency of the capacitance adjustment switches provided to themonitoring-object variable capacitor are monitored.

Likewise, when it is known that there is a difference in switch statechange frequency among the plurality of capacitance adjustment switchesprovided to the monitoring-object variable capacitor, there is no needto use all the capacitance adjustment switches provided to themonitoring-object variable capacitor as monitoring-object switches; aconfiguration may be adopted in which only a capacitance adjustmentswitch that is known to have a high switch state change frequency isused as a monitoring-object switch.

By adopting a configuration in which the switch state change frequencyof the capacitance adjustment switch that is most prone to require rapidprotection is monitored, and temperature increase suppression control isperformed for the capacitance adjustment switch selected as aprotection-object switch when the switch state change frequency thereofis equal to or greater than the evaluation reference value, it ispossible to achieve reliable protection of the capacitance adjustmentswitches constituting the matching circuit. By monitoring the switchstate change frequency of only some of the capacitance adjustmentswitches provided to the matching circuit, it is possible to simplifythe processing for detecting the switch state change frequency andevaluating whether the switch state change frequency is equal to orgreater than the set evaluation reference.

The switch state change frequency of a capacitance adjustment switch canalso be detected by providing the capacitance adjustment switch with aswitch state detection means for detecting whether the capacitanceadjustment switch is in the ON state or the OFF state and counting thenumber of times that a change in the switch state of the capacitanceadjustment switch is detected by the switch state detection means in aset evaluation reference time; however, when the switch state changefrequency is detected by such a method, a switch state detection meansneed only be provided to a portion of the capacitance adjustmentswitches used as monitoring-object switches when only some of thecapacitance adjustment switches are used as monitoring-object switches,and a structure of the matching circuit can therefore be prevented frombecoming complex.

Even when at least one variable capacitor provided to the matchingcircuit 31 is designated as a monitoring-object variable capacitor andat least one of the capacitance adjustment switches provided to themonitoring-object variable capacitor is designated as amonitoring-object switch, it remains the case that at least one of thecapacitance adjustment switches provided to the matching circuit 31 isdesignated as a monitoring-object switch.

In the present invention, the switch state evaluation unit 32B is notprecluded from being configured so that all of the variable capacitorsprovided to the matching circuit 31 are designated as monitoring-objectvariable capacitors, all of the capacitance adjustment switches providedto the variable capacitors, or at least one capacitance adjustmentswitch that is known to have a high switch state change frequency fromamong the capacitance adjustment switches provided to the variablecapacitors is designated as a monitoring-object switch, and anevaluation is made that at least one capacitance adjustment switchprovided to the matching circuit is in a state requiring suppression ofa temperature increase when the switch state change frequency of atleast one monitoring-object switch is evaluated as being equal to orgreater than the evaluation reference value.

<Structure of the Switch State Evaluation Unit Used in the PresentEmbodiment>

As described above, it is possible to designate only some of thecapacitance adjustment switches provided to the matching circuit 31 asmonitoring-object switches in the present invention, but in thefollowing description, the two variable capacitors VC1 and VC2 providedto the matching circuit 31 are both designated as monitoring-objectvariable capacitors, all of the capacitance adjustment switches S1-Snprovided to the monitoring-object variable capacitors are designated asmonitoring-object switches, and the switch state change frequency of themonitoring-object switches is determined by counting the number of timesthat the matching calculation unit 32A changes the target switch stateof the capacitance adjustment switches S1-Sn in the set evaluationreference time.

As described above, the matching calculation unit 32A used in thepresent embodiment is configured so that the first through n^(th) digitsof an n-bit binary number, the first digit and n^(th) digit thereofbeing, respectively, the least significant digit and the mostsignificant digit thereof, are made to correspond respectively to thefirst through n^(th) capacitors C1-Cn, and the target switch state to beattained by the first through n^(th) capacitance adjustment switches isindicated by whether each of the first through n^(th) digits of then-bit binary number are 1 or 0.

In the present embodiment, noting that the n-bit binary number shows acombination pattern of switch states of the first through n^(th)capacitance adjustment switches S1-Sn, the switch state evaluation unit32B is configured so as to evaluate that at least one of the capacitanceadjustment switches provided to the matching circuit 31 is in a staterequiring suppression of a temperature increase when the number of timesthat the n-bit binary number changes in the set evaluation referencetime is equal to or greater than the evaluation reference value.

<Switch Control Unit>

The switch control unit 32C is constituted from a switch control means32C1 for controlling the ON/OFF state of the capacitance adjustmentswitches provided to the matching circuit, and a temperature increasesuppression control means 32C2 for controlling temperature increasesuppression. Here, the switch control means 32C1 is a means forcontrolling the ON/OFF state of the first through n^(th) capacitanceadjustment switches S1-Sn of the variable capacitors, and in a steadystate, the switch control means 32C1 controls the first through n^(th)capacitance adjustment switches S1-Sn of the variable capacitors so asto cause the states of the capacitance adjustment switches to coincidewith the target switch state determined by the matching calculation unit32A.

The temperature increase suppression control means 32C2 is a means forissuing a temperature increase suppression control execution command tothe switch control means 32C1, designating at least one of thecapacitance adjustment switches S1-Sn provided to the matching circuit31 as a protection-object switch, and causing the switch control means32C1 to perform control (temperature increase suppression control) forsuppressing a temperature increase in the protection-object switch for aset temperature increase suppression period when an evaluation is madeby the switch state evaluation unit 32B that at least one of the seriesof capacitance adjustment switches S1-Sn provided to the matchingcircuit 31 is in a state requiring suppression of a temperatureincrease. When only some of the series of capacitance adjustmentswitches S1-Sn provided to the matching circuit 31 are designated asprotection-object switches, the switch control means 32C1 performstemperature increase suppression control for the protection-objectswitches when the temperature increase suppression control executioncommand is issued from the temperature increase suppression controlmeans, but for capacitance adjustment switches other than theprotection-object switches, the switch control means 32C1 performsswitch control for causing the switch states thereof to coincide withthe target switch state.

<Temperature Increase Suppression Control>

Temperature increase suppression control is performed by stopping theswitching operation of the protection-object switch or by reducing thefrequency of switching operation in the protection-object switch. Whentemperature increase suppression control is performed by stopping theswitching operation of the protection-object switch, the switchingoperation of the protection-object switch can be stopped by stoppingcalculation of the target switch state by the matching calculation unit32A for the temperature increase suppression period, or by fixing theswitch state of the protection-object switch at the state thereofimmediately prior to the start of temperature increase suppressioncontrol.

To perform temperature increase suppression control by reducing thefrequency of switching operation by the protection-object switch, forexample, rather than changing the switch state of the protection-objectswitch each time the matching circuit changes the target switch state ofthe capacitance adjustment switches, the switch state of theprotection-object switch may be changed intermittently, with a timeinterval between changes.

When the parameter that reflects the load-side impedance is sampled at aset sampling period and the matching calculation unit 32A is configuredso as to perform matching calculation each time the parameter issampled, as in the present embodiment, the switch control unit 32C canalso be configured so as to reduce a frequency of switching operation bythe protection-object switch by controlling the matching calculationunit 32A so that the period at which the parameter used by the load-sideimpedance calculation means 32A1 of the matching calculation unit 32A todetermine the load-side impedance is sampled from the high-frequencydetection unit 4 is longer than a set normal sampling period when thetemperature increase suppression control is performed.

An optimum duration of the “temperature increase suppression period” forwhich control (temperature increase suppression control) for suppressinga temperature increase in a capacitance adjustment switch is performedcan be determined, for example, by conducting an experiment in which thecapacitance adjustment switch is turned ON and OFF at high frequency toincrease the temperature thereof to the allowable limit, after which theswitching operation of the capacitance adjustment switch is stopped, ortemperature increase suppression control for reducing the frequency ofthe switching operation is started, and the time is calculated that isrequired for the temperature of the capacitance adjustment switch todecrease to an allowable temperature even when switching operation isresumed after stopping switching operation of the capacitance adjustmentswitch or after the start of temperature increase suppression control.

<Protection-Object Switch>

The protection-object switch is a switch, from among the capacitanceadjustment switches provided to the matching circuit 31, for whichtemperature increase suppression control is performed in order toprevent the switch from being destroyed by an excessive temperatureincrease. The protection-object switch may be all of the capacitanceadjustment switches provided to the matching circuit or a portion of thecapacitance adjustment switches provided to the matching circuit. In apreferred embodiment of the present invention, at least one capacitanceadjustment switch including a capacitance adjustment switch having ahigh probability of reaching a state in which suppression of atemperature increase is required when a state of varying load-sideimpedance is continued is selected as the protection-object switch fromamong the capacitance adjustment switches provided to the matchingcircuit.

From among the series of capacitance adjustment switches provided to thematching circuit 31, when a switch is known in advance to have a highprobability of reaching a state in which suppression of a temperatureincrease is required due to frequent switching ON and OFF when a stateof varying load-side impedance is continued, such a switch should bedesignated as a protection-object switch; however, when it is unclearwhether there is a switch that has a high probability of reaching astate in which suppression of a temperature increase is required due tofrequent switching ON and OFF when a state of varying load-sideimpedance is continued, it is preferred that all of the capacitanceadjustment switches provided to the matching circuit be designated asprotection-object switches.

A switch having a high probability of reaching a state in whichsuppression of a temperature increase is required when a state ofvarying load-side impedance is continued is defined as, for example, aswitch that is turned ON and OFF when the value of a lower-order digitof the capacitance in the variable capacitors is adjusted, from amongthe series of capacitance adjustment switches provided to the variablecapacitors, or a monitoring-object switch that is evaluated by thechange frequency evaluation means as having a switch state changefrequency equal to or greater than the set evaluation reference valuefrom among the monitoring-object switches.

It is sometimes simpler to designate all of the capacitance adjustmentswitches provided to the matching circuit 31 as protection-objectswitches and to perform temperature increase suppression control for allof the capacitance adjustment switches equally than to designate onlysome of the series of capacitance adjustment switches provided to thematching circuit as protection-object switches and to performtemperature increase suppression control thereof. In such a case, fromthe perspective of facilitating temperature increase suppressioncontrol, all of the capacitance adjustment switches provided to thematching circuit can be designated as protection-object switches evenwhen it is possible to specify a capacitance adjustment switch thatrequires temperature increase suppression.

<Operation of the Impedance Matching Device>

The operation of the impedance matching device according to the presentembodiment will be described with reference to FIG. 12. In the followingdescription of operation, all of the capacitance adjustment switchesprovided to the variable capacitors VC1 and VC2 are designated asmonitoring-object switches, and all of the monitoring-object switchesare designated as protection-object switches.

FIG. 12 is a time chart illustrating an example of the operation of theimpedance matching device according to the present embodiment, and FIG.12(A) illustrates the sample pulse Ps generated by a pulse generator notillustrated in the drawing. The pulse Ps is generated at a fixedsampling period t1. FIG. 12(B) illustrates the operation of the matchingcalculation unit 32A, and FIG. 12(C) shows the change in the states ofthe series of capacitance adjustment switches S1-Sn provided to thematching circuit 31 to vary the capacitance of the variable capacitorsprovided to the matching circuit. FIG. 12(D) shows the count value ofthe number of times (ON/OFF count) the switch state of the series ofcapacitance adjustment switches is changed.

When two variable capacitors VC1 and VC2 are provided to the matchingcircuit 31 as in the present embodiment, the variation in the states ofthe capacitance adjustment switches S1-Sn provided to the variablecapacitor VC1 and the variation in the states of the capacitanceadjustment switches S1-Sn provided to the variable capacitor VC2generally differ, but to simplify the description below, the variationin the states of the capacitance adjustment switches S1-Sn provided tothe variable capacitor VC1 and the variation in the states of thecapacitance adjustment switches S1-Sn provided to the variable capacitorVC2 are assumed to be the same.

In FIG. 12(B), “execute” indicates that matching calculation isperformed, and “stop” indicates that matching calculation is stopped. InFIG. 12(C), “maintained” means that the load-side impedance calculatedwhen the sample pulse was generated is unchanged from the load-sideimpedance calculated the last time the sample pulse was generated, andthe matching calculation unit 32A has not changed the target switchstate, and that the ON/OFF states of the series of capacitanceadjustment switches provided to the matching circuit are thereforemaintained. In FIG. 12(C), “changed” means that the combination patternof the switch states of the series of capacitance adjustment switchesprovided to the variable capacitors of the matching circuit has changeddue to variation of the ON/OFF state of at least one of the series ofcapacitance adjustment switches.

In FIG. 12(D), “ON/OFF count” indicates the count value of the number oftimes the switch state of the capacitance adjustment switches ischanged, and “Cs” indicates the set evaluation reference value(reference value that is compared with the change count to evaluatewhether the frequency with which the switch state of the capacitanceadjustment switches is changed is equal to or greater than a setallowable limit). The symbol t2 at the bottom of FIG. 12 indicates theevaluation reference time, and t3 indicates the temperature increasesuppression period.

In the present embodiment, when matching operation of the impedancematching device is started, matching calculation is executed each timethe sample pulse Ps is generated. As a result, when the target switchstate is changed, the combination pattern of switch states of the seriesof capacitance adjustment switches of the matching circuit is changed.The target switch state is a state in which the series of capacitanceadjustment switches provided to the variable capacitors should take inorder for the impedance between the high-frequency power source 1 andthe load 2 to be matched. When the parameter that reflects the load-sideimpedance is sampled from the high-frequency detection unit 4 and theload-side impedance is calculated, and as a result, there is novariation in the load-side impedance and the target switch state is notchanged, the combination pattern of switch states of the series ofcapacitance adjustment switches provided for prescribing the capacitanceof the variable capacitors of the matching circuit is maintained in thesame state as at the previous sampling time.

The count value of a number of changes to the switch state of thecapacitance adjustment switches is incremented each time the switchstate of the capacitance adjustment switches is changed insynchronization with the sample pulse Ps, and when the switch state fromthe previous sampling time is maintained, the count value from theprevious sampling time is maintained.

In the present embodiment, a timer is started at the same time thatmatching operation is started, and an elapsed time is measured, and thetimer is reset each time the elapsed time reaches the set evaluationreference time t2. Each time the evaluation reference time t2 ismeasured by the timer, the change frequency evaluation means 32B1compares the count value (switch state change frequency) of the numberof changes to the switch state of the capacitance adjustment switcheswith the set evaluation reference value Cs, and evaluates whether thecount value of the number of changes is equal to or greater than theevaluation reference value. When the result of the evaluation indicatesthat the count value of the number of changes is less than theevaluation reference value, an evaluation is made that there is noswitch among the capacitance adjustment switches provided to thematching circuit 31 that requires suppression of a temperature increase,and when the count value of the number of changes is equal to or greaterthan the evaluation reference value, an evaluation is made that at leastone of the capacitance adjustment switches provided to the matchingcircuit requires suppression of a temperature increase.

Each time an evaluation is made that at least one of the capacitanceadjustment switches provided to the matching circuit requiressuppression of a temperature increase, the set temperature increasesuppression period t3 is measured, and temperature increase suppressioncontrol is performed for the measured temperature increase suppressionperiod t3.

In the example illustrated in FIG. 12, the matching calculation unit 32Ais configured so as to perform temperature increase suppression controlby stopping the matching calculation for the temperature increasesuppression period t3, as indicated in FIG. 12(B). In thisconfiguration, the number of times that the matching calculation unit32A changes the target switch state and the number of times that theswitch state of the series of capacitance adjustment switches of thematching circuit is changed are the same, and the number of times thatthe switch state of the capacitance adjustment switches is changed cantherefore be counted simply by counting the number of times that thematching calculation unit changes the target switch state. However, thepresent invention is not limited to such a configuration of the matchingcalculation unit, and the matching calculation unit 32A may also beconfigured so that matching calculation is executed also during thetemperature increase suppression period t3, as in the exampleillustrated in FIG. 13. In this configuration, after the temperatureincrease suppression period t3 has elapsed, the target switch state canbe made appropriate for the load-side impedance at the time when controlfor causing the switch state of the capacitance adjustment switches tocoincide with the target switch state is resumed, and error in theimpedance matching can therefore be minimized.

In a case in which matching calculation is executed also during thetemperature increase suppression period each time the sample pulse isgenerated, as illustrated in FIG. 13, by also configuring the changefrequency evaluation means 32B1 so as to stop counting the number oftimes that the matching calculation unit 32A changes the target switchstate during the temperature increase suppression period t3 and to countthe number of times that the matching calculation unit 32A changes thetarget switch state for during the evaluation reference time t2, it ispossible to determine the number of times (switch state changefrequency) the switch state of the series of capacitance adjustmentswitches of the variable capacitors is changed from the number of timesthat the matching calculation unit 32A changes the target switch state.

The evaluation reference value Cs, the evaluation reference time t2, andthe temperature increase suppression period t3 are set on the basis ofexperimentation in consideration of proper values thereof for keepingjunction temperatures of the semiconductor elements constituting thecapacitance adjustment switches within an allowable range, keeping theimpedance matching error in the range necessary for ensuring operationof the load, and keeping reflected power within an allowable range. Ajunction temperature of a capacitance adjustment switch can be estimatedby detecting the surface temperature of the capacitance adjustmentswitch, for example.

When a configuration is adopted in which the switch state evaluationunit 32B is provided for evaluating (evaluating the necessity oftemperature increase suppression) whether at least one of thecapacitance adjustment switches S1-Sn provided to the matching circuit31 is in a state requiring suppression of a temperature increase, atleast one of the capacitance adjustment switches S1-Sn provided to thematching circuit 31 is designated as a protection-object switch when anevaluation is made by the evaluation unit that at least one of thecapacitance adjustment switches S1-Sn provided in the matching circuit31 is in a state requiring suppression of a temperature increase, andtemperature increase suppression control for suppressing a temperatureincrease in the protection-object switch by stopping switching operationof the protection-object switch or reducing the frequency with which theprotection-object switch performs switching operation is performed forthe set temperature increase suppression period, as in the presentembodiment, it is possible to eliminate or limit heat generation fromthe protection-object switch for the duration of the temperatureincrease suppression period and to suppress a temperature increasetherein, and appropriate protection of the capacitance adjustmentswitches can therefore be achieved. For a period other than thetemperature increase suppression period, switch control is alsoperformed for causing the switch state of the series of capacitanceadjustment switches provided to the matching circuit to coincide withthe target switch state determined by the matching calculation unit 32A,and it is therefore possible to protect the capacitance adjustmentswitches without significantly decreasing precision of impedancematching between the high-frequency power source 1 and the load 2.

The matching calculation unit 32A, the change frequency evaluation means32B1, and the switch control unit 32C of the control unit 32 illustratedin FIG. 2 can be realized by causing a microprocessor to execute apredetermined program. FIG. 10 illustrates an example of a processingalgorithm executed by a microprocessor in order to constitute thematching calculation unit 32A, the change frequency evaluation means32B1, and the switch control unit 32C, and is executed every time thesample pulse Ps is generated.

When the algorithm illustrated in FIG. 10 is adopted, in the first stepS01 that occurs when a command to start impedance matching operation isreceived, each component is initialized, the measurement value ta of afirst timer for measuring the time elapsed since the start (orresumption) of matching operation, the measurement value tb of a timerfor measuring the elapsed time in the temperature increase suppressionperiod, the measurement value c of a counter for counting the number oftimes the state of the series of capacitance adjustment switches S1-Snprovided to at least one of the variable capacitors of the matchingcircuit is changed, and a flag F for indicating that the temperatureincrease suppression period is in effect are reset to 0.

The counting value c of the counter is incremented by 1 when the switchstate of the series of capacitance adjustment switches provided toeither one of the variable capacitors VC1 and VC2 is changed, as well aswhen the states of the series of capacitance adjustment switches S1-Snprovided to all of the variable capacitors VC1 and VC2 of the matchingcircuit are changed.

After each component is initialized in step S01, the algorithm proceedsto step S02, an evaluation is made as to whether a command to endmatching operation has been received and when a command of suchdescription has not been received, the algorithm proceeds to step S03and waits until the sample pulse Ps is generated. When an evaluation ismade in step S03 that the sample pulse Ps has been generated, thealgorithm proceeds to step S04, and an evaluation is made as to whetherthe flag F is set to 1. When the result of the evaluation indicates thatthe flag F is not set to 1, the algorithm proceeds to step S05 and themeasurement value ta of the first timer is incremented by 1. Thealgorithm next proceeds to step S06, and matching calculation isperformed which includes a process for calculating the impedance viewedfrom the output terminal of the high-frequency power source 1 toward theload, and a process for determining the state to be assumed by theseries of capacitance adjustment switches S1-Sn provided to the variablecapacitor VC1 and the state to be assumed by the series of capacitanceadjustment switches S1-Sn provided to the variable capacitor VC2 as thetarget switch state of the capacitance adjustment switches S1-Sn of thevariable capacitor VC1 and the target switch state of the capacitanceadjustment switches S1-Sn of the variable capacitor VC2, respectively,in order to match the calculated impedance to the output impedance ofthe high-frequency power source.

After the matching calculation is performed, the algorithm proceeds tostep S07 and an evaluation is made as to whether the target switch stateis changed, and when the target switch state of the capacitanceadjustment switches S1-Sn of the variable capacitor VC1 and the targetswitch state of the capacitance adjustment switches S1-Sn of thevariable capacitor VC2 are both unchanged, the algorithm returns to stepS02. When an evaluation is made in step S07 that the target switch stateof the of the capacitance adjustment switches S1-Sn of the variablecapacitor VC1 and/or the target switch state of the capacitanceadjustment switches S1-Sn of the variable capacitor VC2 has beenchanged, the algorithm proceeds to step S08, and processing is performedfor causing the states of the first through n^(th) capacitanceadjustment switches S1-Sn of the variable capacitor VC1 and the statesof the first through n^(th) capacitance adjustment switches S1-Sn of thevariable capacitor VC2 each to coincide with the target switch state.The algorithm then proceeds to step S09, and the counting value c of thecounter for counting the number of changes to the state of thecapacitance adjustment switches S1-Sn is incremented by 1.

After step S09 is executed, the algorithm proceeds to step S10 and anevaluation is made as to whether the counting value c of the counter isequal to or greater than the evaluation reference value Cs. When theevaluation is not that that C≥Cs, the algorithm returns to step S02, andwhen C≥Cs, the algorithm proceeds to step S11, and an evaluation is madeas to whether the elapsed time ta from the start of the matchingoperation is equal to or greater than the evaluation reference time t2.When the result of the evaluation indicates that the elapsed time ta isnot equal to or greater than the evaluation reference time t2, thealgorithm returns to step S02, and when the elapsed time ta is equal toor greater than the evaluation reference time t2, the algorithm proceedsto step S12, and changing of the states of the capacitance adjustmentswitches S1-Sn of the variable capacitors is stopped (maintained at thecurrent state) and the flag F is set to 1. The algorithm then returns tostep S02 after the measurement value tb of the second timer formeasuring the elapsed time in the temperature increase suppressionperiod is set in step S13 to the set temperature increase suppressionperiod t3.

When the transition to step S02 is made in a state in which the flag Fis set to 1, since the flag F is evaluated as being 1 in step S04, thealgorithm then transitions to step S14 and an evaluation is made as towhether the measurement value tb of the second timer has reached thetemperature increase suppression period t3. When the result of theevaluation is that the measurement value tb of the second timer has notreached the temperature increase suppression period t3, the algorithmproceeds to step S15 and the measurement value tb of the second timer isincremented by 1, and the algorithm returns to step S02. Untilmeasurement value tb of the second timer reaches the set temperatureincrease suppression period t3 the process of stepS02→S03→S04→S14→S15→S02 is repeated in a state in which changing of thestates of the capacitance adjustment switches S1-Sn of the variablecapacitors is stopped, and the state of the capacitance adjustmentswitches S1-Sn of the variable capacitor VC1 and the state of thecapacitance adjustment switches S1-Sn of the variable capacitor VC2 aretherefore maintained unchanged. The state of the capacitance adjustmentswitches S1-Sn of the variable capacitors is thus maintained for the settemperature increase suppression period t3 in the state thereofimmediately prior to the start of the temperature increase suppressionperiod t3.

When the evaluation is made in step S14 that the measurement value tb ofthe second timer has reached the temperature increase suppression periodt3, the algorithm proceeds to step S16 and the flag F is reset to 0,after which the algorithm returns to step S02. The algorithm thenproceeds to step S03, and step S04 is executed when the evaluation ismade in step S03 that the sample pulse Ps has been generated, butbecause the flag F is then evaluated as not being 1 in step S04, thesteps including and subsequent to step S05 are executed, and matchingcalculation and changing of the states of the capacitance adjustmentswitches S1-Sn of the variable capacitors are resumed.

When an evaluation is made that the number of changes to the state ofthe capacitance adjustment switches S1-Sn made in the evaluationreference time t2 is less than the set evaluation reference value Cs, asdescribed above, control is performed for causing the state of thecapacitance adjustment switches S1-Sn to coincide with the changedtarget switch state each time the matching calculation unit changes thetarget switch state, and when an evaluation is made that the number ofchanges made in the evaluation reference time is equal to or greaterthan the set evaluation reference value, control for causing the switchstate of the series of capacitance adjustment switches to coincide withthe target switch state changed by the matching calculation unit isresumed after a change suspension process is performed for suspendingchanging of the state of the capacitance adjustment switches S1-Sn forthe duration of the set temperature increase suppression period t3.

When the algorithm illustrated in FIG. 10 is adopted, steps S05 throughS11 constitute the change frequency evaluation means 32B1, and steps S02through S04 and steps S12 through S16 constitute the switch control unit32C.

In the case that the algorithm illustrated in FIG. 10 is adopted, thematching calculation unit stops the matching calculation during thetemperature increase suppression period t3 and resumes matchingcalculation after the temperature increase suppression period t3 haselapsed, but the matching calculation unit may also be configured so asto perform matching calculation each time the parameter is sampledduring the temperature increase suppression period as well. FIG. 11 is aflowchart illustrating the algorithm of the program executed by themicroprocessor when the control unit is configured so that matchingcalculation is performed each time the parameter is sampled during thetemperature increase suppression period as well.

In the algorithm illustrated in FIG. 11, when the pulse Ps is recognizedin step S03, the algorithm transitions to step S06 and matchingcalculation is performed, and the flag F is then set to 1 in step S04′,after which the measurement value ta of the first timer is incrementedin step S05′. The algorithm illustrated in FIG. 11 is otherwise the sameas the algorithm illustrated in FIG. 10.

The evaluation reference value Cs, the evaluation reference time t2, andthe temperature increase suppression period t3 may be fixed values ormay be changed in accordance with the heat production condition of thecapacitance adjustment switches.

For example, as illustrated in FIG. 3, a configuration may be adopted inwhich a temperature sensor 5 for detecting a temperature that reflectsthe temperature of the series of capacitance adjustment switches of thevariable capacitors, and a temperature increase suppression periodsetting means 6 for setting the temperature increase suppression periodt3 used by the switch control unit 32C in accordance with thetemperature detected by the temperature sensor 5 are provided, and thetemperature increase suppression period t3 is varied in accordance withthe temperature of the capacitance adjustment switches. The temperatureincrease suppression period setting means 6 in this case can beconstituted from a sampling means for sampling the output of thetemperature sensor 5 at a fixed period, a temperature increasesuppression period calculation means for calculating the temperatureincrease suppression period for the sampled temperature, and a storagemeans for storing the calculated temperature increase suppression periodin memory.

The temperature increase suppression period can be calculated byretrieving a temperature increase suppression period calculation map forthe temperature sampled by the sampling means. The temperature increasesuppression period calculation map is made so that the temperatureincrease suppression period t3 is made longer the higher the temperaturedetected by the temperature sensor is.

In this case, the temperature increase suppression control means 32C2reads the newest temperature increase suppression period t3 stored inthe memory when the switch state evaluation unit 32B has evaluated thatthere is a switch that requires suppression of a temperature increaseamong the capacitance adjustment switches provided to the matchingcircuit, sets the read temperature increase suppression period t3 in thetimer, and causes temperature increase suppression control to beperformed as the timer is measuring the set temperature increasesuppression period t3.

The temperature that reflects the temperature of the first throughn^(th) capacitance adjustment switches S1-Sn may be the temperature of asubstrate on which the first through n^(th) capacitance adjustmentswitches S1-Sn are mounted, or the temperature of a heat sink or thelike devised to dissipate heat from the capacitance adjustment switches,for example.

When such a configuration is adopted, the temperature increasesuppression period for suspending changing of the switch state of theseries of capacitance adjustment switches can be set to an appropriateduration in accordance with the temperature of the capacitanceadjustment switches, and it is therefore possible to achieve reliableprotection of the series of capacitance adjustment switches whilesuppressing a decrease in the precision of impedance matching.

As illustrated in FIG. 4, a configuration may also be adopted in which atemperature sensor 5 for detecting a temperature that reflects thetemperature of the series of capacitance adjustment switches of thevariable capacitors, and an evaluation reference value setting means 7for setting the evaluation reference value used by the change frequencyevaluation means 32B1 in accordance with the temperature detected by thetemperature sensor 5 are provided, and the evaluation reference value isvaried in accordance with the temperature of the series of capacitanceadjustment switches. The evaluation reference value setting means 7 inthis case is configured so as to make the evaluation reference valuesmaller the higher the temperature detected by the temperature sensor 5is. The evaluation reference value setting means 7 can be configured soas to calculate the evaluation reference value as needed for thetemperature detected by the temperature sensor 5 and cause thecalculated evaluation reference value to be stored in memory, in thesame manner as in the temperature increase suppression period settingmeans illustrated in FIG. 3.

When such a configuration is adopted, changing of the switch state ofthe capacitance adjustment switches can be suspended more often thehigher the temperature of the series of capacitance adjustment switchesis, and changing of the switch state of the capacitance adjustmentswitches can be suspended less often when the temperature of the seriesof capacitance adjustment switches is not so high. Changing of theswitch state of the capacitance adjustment switches can therefore besuspended with a frequency that is appropriate for the temperature ofthe series of capacitance adjustment switches, and it is possible toachieve reliable protection of the series of capacitance adjustmentswitches while suppressing a decrease in the precision of impedancematching.

As illustrated in FIG. 5, a configuration may also be adopted in which atemperature sensor 5 for detecting a temperature that reflects thetemperature of the series of capacitance adjustment switches, and anevaluation reference time setting means 8 for setting the evaluationreference time used by the change frequency evaluation means 32B1 inaccordance with the temperature detected by the temperature sensor 5 areprovided, and the evaluation reference time is varied in accordance withthe temperature of the capacitance adjustment switches. The evaluationreference time setting means 8 in this case is configured so as to makethe evaluation reference time shorter the higher the temperaturedetected by the temperature sensor 5 is.

Through this configuration as well, because changing of the switch stateof the capacitance adjustment switches can be suspended with a frequencythat is appropriate for the temperature of the series of capacitanceadjustment switches, it is possible to achieve reliable protection ofthe capacitance adjustment switches while suppressing a decrease in theprecision of impedance matching.

Furthermore, as illustrated in FIG. 6, a configuration may be adopted inwhich a temperature sensor 5 for detecting a temperature that reflectsthe temperature of the series of capacitance adjustment switches, atemperature increase suppression period setting means 6 for setting thetemperature increase suppression period used by the switch control unit32C in accordance with the temperature detected by the temperaturesensor 5, and an evaluation reference value setting means 7 for settingthe evaluation reference value used by the change frequency evaluationmeans 32B1 in accordance with the temperature detected by thetemperature sensor 5 are furthermore provided, and the temperatureincrease suppression period and the evaluation reference value arevaried in accordance with the temperature of the series of capacitanceadjustment switches. The temperature increase suppression period settingmeans 6 in this case is configured so as to make the temperatureincrease suppression period longer the higher the temperature detectedby the temperature sensor 5 is, and the evaluation reference valuesetting means 7 is configured so as to make the evaluation referencevalue smaller the higher the temperature detected by the temperaturesensor 5 is.

When such a configuration is adopted, not only can the period forsuspending changing of the switch state of the capacitance adjustmentswitches be set to an appropriate duration in accordance with thetemperature of the capacitance adjustment switches, but changing of theswitch state of the capacitance adjustment switches can also besuspended with an appropriate frequency in accordance with thetemperature of the series of capacitance adjustment switches, and it istherefore possible to achieve reliable protection of the series ofcapacitance adjustment switches while suppressing a decrease in theprecision of impedance matching.

Furthermore, as illustrated in FIG. 7, a configuration may be adopted inwhich a temperature sensor 5 for detecting a temperature that reflectsthe temperature of the series of capacitance adjustment switches, atemperature increase suppression period setting means 6 for setting thetemperature increase suppression period used by the switch control unit32C in accordance with the temperature detected by the temperaturesensor 5, and an evaluation reference time setting means 9 for settingthe evaluation reference time used by the change frequency evaluationmeans 32B1 in accordance with the temperature detected by thetemperature sensor 5 are provided, and the temperature increasesuppression period t3 and the evaluation reference time t2 varied inaccordance with the temperature of the series of capacitance adjustmentswitches. The temperature increase suppression period setting means 6 inthis case is configured so as to make the temperature increasesuppression period longer the higher the temperature detected by thetemperature sensor 5 is, and the evaluation reference time setting means9 is configured so as to make the evaluation reference time shorter thehigher the temperature detected by the temperature sensor 5 is.

It is also the case that when such a configuration is adopted, changingof the switch state of the capacitance adjustment switches can besuspended more often the higher the temperature of the series ofcapacitance adjustment switches is, and changing of the switch state ofthe capacitance adjustment switches can be suspended less often when thetemperature of the series of capacitance adjustment switches is not sohigh. Changing of the switch state of the capacitance adjustmentswitches can therefore be suspended with a frequency that is appropriatefor the temperature of the capacitance adjustment switches, and it ispossible to achieve reliable protection of the capacitance adjustmentswitches while suppressing a decrease in the precision of impedancematching.

<Modification of the Switch State Evaluation Unit>

In the embodiments described above, an evaluation is made as to whetherat least one monitoring-object switch is in a state requiringsuppression of a temperature increase on the basis of whether the switchstate change frequency of the capacitance adjustment switches is equalto or greater than an evaluation reference value; however, the switchstate evaluation unit 32B may also be configured so as to evaluatewhether at least one monitoring-object switch is in a state requiringsuppression of a temperature increase by evaluating whether theoccurrence frequency of variation in the load-side impedance is equal toor greater than an evaluation reference value.

FIG. 8 illustrates an embodiment in which the switch state evaluationunit 32B is configured as described above. In the example illustrated inFIG. 8, the switch state evaluation unit 32B is constituted from aload-side impedance occurrence frequency detection means 32B2 and aload-side impedance variation occurrence frequency evaluation means32B3. Here, the load-side impedance occurrence frequency detection means32B2 is a means for detecting, as a load-side impedance variationoccurrence frequency, a number of times that the impedance viewed fromthe output terminal of the high-frequency power source 1 toward the load2 undergoes a variation greater than or equal to a set size in a setevaluation reference time, and the load-side impedance variationoccurrence frequency evaluation means 32B3 is a means for evaluatingwhether the load-side impedance variation occurrence frequency detectedby the load-side impedance occurrence frequency detection means 32B2 isequal to or greater than a set evaluation reference value. The switchstate evaluation unit 32B is configured so as to evaluate that at leastone of the capacitance adjustment switches provided to the matchingcircuit 31 is in a state requiring suppression of a temperature increasewhen an evaluation is made by the load-side impedance variationoccurrence frequency evaluation means 32B3 that the load-side impedancevariation occurrence frequency is equal to or greater than the setevaluation reference value.

The load-side impedance occurrence frequency detection means 32B2illustrated in FIG. 8 is configured so that each time the matchingcalculation unit 32A samples the parameter that reflects the impedance(load-side impedance) viewed from the output terminal of thehigh-frequency power source 1 to the load-side circuit, a differencebetween a parameter at an immediately preceding sampling thereof and aparameter at a current sampling thereof is detected as the parametervariation amount, and a number of times that a parameter variationamount equal to or greater than a set size is detected in a setevaluation reference time is designated as the load-side impedancevariation occurrence frequency. A reflection coefficient, for example,can be used as a parameter that reflects the load-side impedance.

The evaluation reference value and the evaluation reference time mayhave fixed values, but in order to achieve reliable protection of aprotection-object switch, the evaluation reference value and theevaluation reference time may be varied with respect to an appropriateparameter. For example, a temperature sensor may be provided fordetecting a temperature that reflects the temperature of the capacitanceadjustment switches provided to the matching circuit, and the evaluationreference value may be made smaller the higher the temperature detectedby the temperature sensor is, or the evaluation reference time may bemade shorter the higher the temperature detected by the temperaturesensor is.

In the example illustrated in FIG. 8, a temperature sensor 5 fordetecting a temperature that reflects the temperature of the capacitanceadjustment switches, a temperature increase suppression period settingmeans 6 for setting the temperature increase suppression period t3 withrespect to the temperature detected by the temperature sensor 5,evaluation reference value setting means 8 for setting the evaluationreference value for comparison with the load-side impedance variationoccurrence frequency with respect to the temperature detected by thetemperature sensor 5, and an evaluation reference time setting means 9for setting the evaluation reference time used by the load-sideimpedance occurrence frequency detection means 32B2 in accordance withthe temperature detected by the temperature sensor 5 are provided.

The temperature increase suppression period setting means 6 isconfigured so as to make the temperature increase suppression periodlonger the higher the temperature detected by the temperature sensor 5is, and the evaluation reference value setting means 8 is configured soas to make the evaluation reference value used by the load-sideimpedance occurrence frequency detection means 32B2 smaller the higherthe temperature detected by the temperature sensor 5 is.

<Other Modification of the Switch State Evaluation Unit>

Another modification of the switch state evaluation unit 32B that can beused in an embodiment of the present invention is described below withreference to FIG. 9. Also in the example illustrated in FIG. 9, atemperature sensor 5 for detecting a temperature that reflects thetemperature of the capacitance adjustment switches is provided, and theswitch state evaluation unit 32B is configured so that when thetemperature detected by the temperature sensor 5 is equal to or greaterthan a set evaluation reference value, an evaluation is made that atleast one of the capacitance adjustment switches provided to thematching circuit 31 is in a state requiring suppression of a temperatureincrease. Also in the example illustrated in FIG. 9, a temperatureincrease suppression period setting means 6 is provided for setting thetemperature increase suppression period used by the switch control unit32C, in accordance with the temperature detected by the temperaturesensor 5, and the temperature increase suppression period is set to alonger duration the higher the temperature detected by the temperaturesensor 5 is.

OTHER EMBODIMENTS

In the above embodiments, the matching calculation unit 32A isconfigured so as to calculate, as the target capacitance, the value thatthe capacitance of the variable capacitors VC1 and VC2 should have so asto match together the output impedance of the high-frequency powersource and the impedance of the circuit (load-side impedance) viewedfrom the output terminal of the high-frequency power source toward theload, and is configured so as to determine, as the target switch state,the state that the series of capacitance adjustment switches S1-Sn ofthe variable capacitors VC1 and VC2 should have in order to set thecapacitance of the variable capacitors to the calculated targetcapacitance. However, it is sufficient ultimately for the matchingcalculation unit 32A to be capable of determining the state to beassumed by the capacitance adjustment switches S1-Sn of the variablecapacitors, and the constitution of the matching calculation unit 32A isnot limited to the examples described in the above embodiments.

For example, a configuration may be adopted in which a map is preparedin advance for assigning a relationship between the load-side impedanceand the target switch state to be assumed by the capacitance adjustmentswitches S1-Sn of the variable capacitors, and the target switch stateis determined by retrieving the map for the load-side impedance.

In the above description, the load-side impedance is calculated eachtime the parameter that reflects the load-side impedance is sampled, andthe capacitance of the variable capacitors that is needed in order tomatch the calculated load-side impedance to the output impedance of thehigh-frequency power source is calculated. However, the method ofdetermining the capacitance of the variable capacitors that is necessaryin order to match the load-side impedance to the output impedance of thehigh-frequency power source 1 is not limited to the examples describedin the above embodiments.

For example, the present invention is also applicable when a method isemployed in which a high-frequency detection unit (e.g., a directionalcoupler) for outputting a traveling-wave power detection signal and areflected-wave power detection signal is used as the high-frequencydetection unit 4, and the capacitance of the variable capacitors isdetermined so that the reflection coefficient calculated from thesampled traveling-wave power detection signal and the reflected-wavepower detection signal is set to zero.

In the above description, PIN diodes are used as the first throughn^(th) capacitance adjustment switches S1-Sn provided to the variablecapacitors, but the first through n^(th) capacitance adjustment switchesS1-Sn may be any capacitance adjustment switches that can be switched ONand OFF at high speed, and MOSFETs, for example, can be used instead ofPIN diodes.

In the above embodiments, an L-type circuit constituted from oneinductor and two variable capacitors is used as the matching circuit 31,as illustrated in FIG. 1, but the constitution of the matching circuit31 is not limited to the example illustrated in FIG. 1; the presentinvention can be broadly applied to various types of matching circuitsused to match impedance by adjusting the capacitance of a variablecapacitor. The number of variable capacitors provided to the matchingcircuit is also arbitrary.

The load 2 is a plasma load in the above description, but the load 2 towhich high-frequency electric power is supplied from the high-frequencypower source 1 is not limited to a plasma load in the present invention.

In the examples illustrated in FIGS. 12 and 13, the switch control unitis configured so as to perform temperature increase suppression controlfor the temperature increase suppression period t3 after the evaluationreference time t2 has elapsed, even when the switch state changefrequency has reached the evaluation reference value before theevaluation reference time t2 has elapsed; however, the switch controlunit 32C may also be configured so that when the switch state changefrequency reaches the evaluation reference value before the evaluationreference time t2 has elapsed, temperature increase suppression controlis performed immediately without waiting for the evaluation referencetime t2 to elapse.

Various embodiments of the impedance matching device according to thepresent invention are described above, but the embodiments describedabove are merely illustrative of possible configurations of thecomponents of the present invention when carrying out the same, and thepresent invention is not limited to being configured as described in theembodiments. For example, in the above description, when a temperaturesensor for detecting a temperature that reflects the temperature of thecapacitance adjustment switches is provided, and the temperatureincrease suppression period is set in accordance with the temperaturedetected by the temperature sensor, the temperature increase suppressionperiod, the evaluation reference value, and the like are calculated asneeded for the temperature detected by the temperature sensor. However,the present invention is not limited to such a configuration, and thetemperature increase suppression period may be determined for thetemperature detected by the temperature sensor when temperature increasesuppression control is performed. Likewise, rather than determining theevaluation reference time or the evaluation reference value as neededfor the temperature detected by the temperature sensor, a configurationmay be adopted in which the evaluation reference time or the evaluationreference value is determined for the temperature detected by thetemperature sensor when the evaluation is made as to whether amonitoring-object switch is in a state requiring suppression of atemperature increase.

In the above description, the switch control unit 32C is constitutedfrom a switch control means 32C1 and a temperature increase suppressioncontrol means 32C2, as illustrated in FIG. 2, for example, and in asteady state in which an evaluation is made by the switch stateevaluation unit 32B that a monitoring-object switch is not in a staterequiring suppression of a temperature increase, the switch stateevaluation unit 32B is caused to perform control for making the statesof the capacitance adjustment switches coincide with the target switchstate, and when an evaluation is made by the switch state evaluationunit 32B that at least one monitoring-object switch is in a staterequiring suppression of a temperature increase, a temperature increasesuppression control execution command is issued from the temperatureincrease suppression control means 32C2 to the switch control unit 32C,and the switch control means 32C1 is caused to execute control forsuppressing a temperature increase in the protection-object switch.However, the switch control unit 32C need only be configured so as toperform control for causing the states of the capacitance adjustmentswitches to coincide with the target switch state in a steady state, andto perform temperature increase suppression control for theprotection-object switch when at least one monitoring-object switch isevaluated as requiring suppression of a temperature increase, and theconfiguration of the switch control unit 32C is not limited to theconfiguration in the above description.

For example, a configuration may be adopted in which the switch controlunit 32C is constituted from a “steady-state switch control means” and a“temperature increase suppression switch control means,” and when in asteady state in which there is no need for temperature increasesuppression control, control for causing the states of the capacitanceadjustment switches to coincide with the target switch state isperformed by the steady-state switch control means, and when the switchstate evaluation unit 32B evaluates that at least one monitoring-objectswitch is in a state requiring suppression of a temperature increase,control for suppressing a temperature increase in the protection-objectswitch is performed by the temperature increase suppression switchcontrol means.

INDUSTRIAL APPLICABILITY

The present invention is an electronically controlled impedance matchingdevice for matching an output impedance of a high-frequency power sourceand an impedance viewed from an output terminal of the high-frequencypower source to a load-side circuit. This is achieved through the use ofa matching circuit provided with variable capacitors in which acapacitance thereof is adjusted by an ON/OFF operation of switchescomprising semiconductor elements in order to increase a speed ofmatching. The impedance matching device is configured so that thecapacitance adjustment switches provided to the variable capacitors canbe prevented from excessively increasing in temperature and beingdestroyed when the switches are turned ON and OFF at high frequency inconjunction with variation of a load-side impedance. The presentinvention makes it possible for a matching operation to more closelyfollow variations in the load-side impedance, while providing highreliability to an operation of the capacitance adjustment switches ofthe variable capacitors. Highly precise impedance matching can thereforebe achieved and electric power can be efficiently supplied to a loadeven when the impedance of the load varies at high frequency.Consequently, the present invention can increase applicability of anelectronically controlled impedance matching device in industrial fieldsin which there is a need to supply high-frequency electric power to aload that has frequent variations in impedance, such as a plasma load.

EXPLANATION OF NUMERALS AND CHARACTERS

-   -   1 high-frequency power source    -   2 load    -   3 impedance matching device    -   4 high-frequency detection unit    -   31 matching circuit    -   32 control unit    -   32A matching calculation unit    -   32A1 load-side impedance calculation means    -   32A2 capacitance calculation means    -   32A3 target switch state determination means    -   32B switch state evaluation unit    -   32B1 change frequency evaluation means    -   32B2 load-side impedance variation occurrence frequency        detection means    -   32B3 load-side impedance variation occurrence frequency        evaluation means    -   32C switch control unit    -   5 temperature sensor    -   6 temperature increase suppression period setting means    -   8 evaluation reference time setting means    -   9 evaluation reference time setting means    -   L1 inductor    -   VC1, VC2 variable capacitors    -   C1-Cn first through n^(th) capacitors    -   S1-Sn first through n^(th) capacitance adjustment switches

1. An impedance matching device for matching an output impedance of ahigh-frequency power source and a load-side impedance, which is animpedance of a circuit viewed from an output terminal of thehigh-frequency power source to a load-side circuit, said impedancematching device comprising: a matching circuit disposed between saidhigh-frequency power source and a load, the matching circuit beingprovided with at least one variable capacitor having a structure inwhich a plurality of capacitance elements are connected in parallel, thecapacitance elements being constituted from a capacitor and acapacitance adjustment switch connected in series, and the capacitanceadjustment switch comprising a semiconductor element; a matchingcalculation unit for performing, at a set period, a matching calculationfor determining, as a target switch state, a state in which thecapacitance adjustment switches provided to said matching circuit shouldtake in order for the output impedance of said high-frequency powersource and said load-side impedance to be matched; a switch control unitfor performing control for causing switch states of the capacitanceadjustment switches provided to said matching circuit to coincide withsaid target switch state; and a switch state evaluation unit forevaluating whether at least one of the capacitance adjustment switchesprovided to said matching circuit is in a state requiring suppression ofa temperature increase; said switch control unit being configured sothat when an evaluation is made by said switch state evaluation unitthat at least one of the capacitance adjustment switches provided tosaid matching circuit is in a state requiring suppression of atemperature increase, the at least one capacitance adjustment switchprovided to said matching circuit is designated as a protection-objectswitch, and temperature increase suppression control for suppressing atemperature increase in said protection-object switch by stoppingswitching operation of said protection-object switch or reducing afrequency with which said protection-object switch performs switchingoperation is performed for a set temperature increase suppressionperiod.
 2. The impedance matching device of claim 1, wherein: saidprotection-object switch is at least one capacitance adjustment switch,from among the capacitance adjustment switches provided to said matchingcircuit, including a switch having a high probability of reaching astate in which suppression of a temperature increase is required when astate of varying load-side impedance is continued.
 3. The impedancematching device of claim 1, wherein: said matching calculation unit isconfigured so as to sample, at a set sampling period, a parameter thatreflects an impedance viewed from the output terminal of saidhigh-frequency power source toward the load, and to perform saidmatching calculation each time said parameter is sampled.
 4. Theimpedance matching device of claim 1, wherein: said switch stateevaluation unit is provided with change frequency evaluation means forevaluating whether a switch state change frequency of amonitoring-object switch is equal to or greater than a set evaluationreference value, said monitoring-object switch being at least one of thecapacitance adjustment switches provided to said matching circuit, andthe switch state change frequency being a number of times that a switchstate of the monitoring-object switch is changed from an ON state to anOFF state or from the OFF state to the ON state in a set evaluationreference time, and the switch state evaluation unit is configured so asto evaluate that at least one of the capacitance adjustment switchesprovided to said matching circuit is in a state requiring suppression ofa temperature increase when an evaluation is made by said changefrequency evaluation means that the switch state change frequency of atleast one monitoring-object switch is equal to or greater than saidevaluation reference value.
 5. The impedance matching device of claim 4,wherein: said switch state evaluation unit is configured so as todesignate at least one variable capacitor provided to said matchingcircuit as a monitoring-object variable capacitor, and to designate atleast one capacitance adjustment switch provided to themonitoring-object variable capacitor as said monitoring-object switch.6. The impedance matching device of claim 4, wherein: the switch statechange frequency of said monitoring-object switch is a number of timesthat the switch state of the monitoring-object switch is changed in aset evaluation reference time.
 7. The impedance matching device of claim4, wherein: the switch state change frequency of said monitoring-objectswitch is a number of times that said matching calculation unit changesthe target switch state of said monitoring-object switch in saidevaluation reference time.
 8. The impedance matching device of claim 3,wherein: said switch state evaluation unit is provided with load-sideimpedance occurrence frequency detection means for detecting, as aload-side impedance variation occurrence frequency, a number of timesthat a variation greater than or equal to a set size occurs in saidload-side impedance in a set evaluation reference time, and load-sideimpedance variation occurrence frequency evaluation means for evaluatingwhether the detected load-side impedance variation occurrence frequencyis equal to or greater than a set evaluation reference value, and saidswitch state evaluation unit is configured so as to evaluate that atleast one of the capacitance adjustment switches provided to saidmatching circuit is in a state requiring suppression of a temperatureincrease when an evaluation is made by said load-side impedancevariation occurrence frequency evaluation means that the load-sideimpedance variation occurrence frequency is equal to or greater than theset evaluation reference value.
 9. The impedance matching device ofclaim 8, wherein: said load-side impedance variation occurrencefrequency detection means is configured so that each time said matchingcalculation unit samples the parameter that reflects the impedanceviewed from the output terminal of said high-frequency power sourcetoward the load, a difference between a parameter at an immediatelypreceding sampling thereof and a parameter at a current sampling thereofis detected as a parameter variation amount, a number of times that aparameter variation amount equal to or greater than a set size isdetected in said evaluation reference time being designated as saidload-side impedance variation occurrence frequency.
 10. The impedancematching device of claim 1, wherein: first through n^(th) capacitors andfirst through n^(th) capacitance adjustment switches connected in seriesto the first through n^(th) capacitors, respectively, are provided tothe variable capacitors provided to said matching circuit; said matchingcalculation unit is configured so that first through n^(th) digits of ann-bit binary number, the first digit and n^(th) digit thereof being,respectively, a least significant digit and a most significant digitthereof, are made to correspond respectively to said first throughn^(th) capacitors, and the target switch state to be attained by saidfirst through n^(th) capacitance adjustment switches is indicated bywhether each of the first through n^(th) digits of the n-bit binarynumber are 1 or 0; and said switch state evaluation unit is configuredso as to evaluate that at least one of the capacitance adjustmentswitches provided to said matching circuit is in a state requiringsuppression of a temperature increase when a number of times that then-bit binary number changes in the set evaluation reference time isequal to or greater than a set evaluation reference value.
 11. Theimpedance matching device of claim 4, wherein: a temperature sensor fordetecting a temperature that reflects a temperature of the capacitanceadjustment switches provided to said matching circuit, and evaluationreference value setting means for setting the evaluation reference valueused by said switch state evaluation means in accordance with thetemperature detected by said temperature sensor are further provided;and said evaluation reference value setting means is configured so as tomake said evaluation reference value smaller the higher the temperaturedetected by said temperature sensor is.
 12. The impedance matchingdevice of claim 4, wherein: a temperature sensor for detecting atemperature that reflects a temperature of the capacitance adjustmentswitches provided to said matching circuit, and evaluation referencetime setting means for setting the evaluation reference time used bysaid switch state evaluation means in accordance with the temperaturedetected by said temperature sensor are further provided; and saidevaluation reference time setting means is configured so as to make saidevaluation reference time shorter the higher the temperature detected bysaid temperature sensor is.
 13. The impedance matching device of claim4, wherein: a temperature sensor for detecting a temperature thatreflects a temperature of the capacitance adjustment switches providedto said matching circuit, and temperature increase suppression periodsetting means for setting said temperature increase suppression periodin accordance with the temperature detected by said temperature sensorare further provided; and said temperature increase suppression periodsetting means is configured so as to make said temperature increasesuppression period longer the higher the temperature detected by saidtemperature sensor is.
 14. The impedance matching device of claim 11,wherein: temperature increase suppression period setting means forsetting said temperature increase suppression period in accordance withthe temperature detected by said temperature sensor is further provided;and said temperature increase suppression period setting means isconfigured so as to make said temperature increase suppression periodlonger the higher the temperature detected by said temperature sensoris.
 15. The impedance matching device of claim 1, wherein: a temperaturesensor for detecting a temperature that reflects a temperature of thecapacitance adjustment switches provided to said matching circuit isprovided; and said switch state evaluation unit is configured so as toevaluate that at least one of the capacitance adjustment switchesprovided to said matching circuit is in a state requiring suppression ofa temperature increase when the temperature detected by said temperaturesensor is equal to or greater than a set evaluation reference value. 16.The impedance matching device of claim 3, wherein: said switch controlunit is configured so as to reduce a frequency of switching operation bysaid protection-object switch by causing said matching calculation unitto sample said parameter at a period longer than said set samplingperiod when said temperature increase suppression control is performed.17. The impedance matching device of claim 1, wherein: said switchcontrol unit is configured so that all of the capacitance adjustmentswitches provided to said matching circuit are designated as saidprotection-object switches.
 18. The impedance matching device of claim4, wherein: said switch control unit is configured so that, from amongsaid monitoring-object switches, a monitoring-object switch that isevaluated by said change frequency evaluation means as having a switchstate change frequency equal to or greater than the set evaluationreference value is designated as said protection-object switch.
 19. Theimpedance matching device of claim 4, wherein: said change frequencyevaluation means is configured so that in a process of evaluatingwhether the switch state change frequency of said monitoring-objectswitch is equal to or greater than the set evaluation reference value,when the switch state change frequency reaches the evaluation referencevalue before said evaluation reference time has elapsed, the changefrequency evaluation means evaluates that the switch state changefrequency of said monitoring-object switch is equal to or greater thanthe set evaluation reference value without waiting for said evaluationreference time to elapse.
 20. The impedance matching device of claim 1,characterized in that said matching calculation unit is configured so asto stop said matching calculation for said temperature increasesuppression period and resume said matching calculation after saidtemperature increase suppression period has elapsed.
 21. The impedancematching device of claim 1, characterized in that said matchingcalculation unit is configured so as to perform said matchingcalculation also during said temperature increase suppression period.